The cooling of various parts of dynamoelectric machines has long been recognized as being advantageous. By cooling various components, the capacity of a given machine is increased because the heat generated during operation which might otherwise destroy or damage the machine at a given capacity level is carried away by the coolant.
This increase in capacity is particularly advantageous in aircraft generators. In such a use, the weight of the generator is a substantial concern. Thus, for a desired capacity necessary to meet electrical consumption requirements on an aircraft, the weight of the generator may be minimized by increasing the effectiveness of its cooling system. For instance, an improved cooling system for an aircraft generator is shown in copending application Ser. No. 755,255, filed July 15, 1985 and assigned to the assignee of this invention.
Typical generators employed in aircraft are so-called "brushless" generators. They frequently include a stator which includes a main armature, an exciter field, and a permanent magnet generator armature. The rotor includes a permanent magnet field, an exciter armature and a main field winding. In addition, the rotor will include a full or a half wave rectifier, usually a full wave rectifier which interconnects the exciter armature and the main field winding to allow the former to energize the latter while at the same time rectifying the alternating current generated in the exciter armature to direct current before it is applied to the main field winding.
Such generators may have a relatively complex network of coolant passages throughout the generator housing between various compartments and areas about the various components of the generator, as described above. For instance, to adequately cool the rotor, it is necessary that both the exciter armature and the main field winding be cooled. It is also necessary to cool the rectifier. All of the coolant passages are provided with various types of seals to contain the flow of the oil within the coolant passages. The housing of the generator normally has several locations forming isolated compartments into which the seals are designed to prevent migration or leakage of the cooling oil. However, regardless of how efficient the seals may be designed, some cooling oil nevertheless leaks into the isolated compartments and, therefrom, to operative areas of the generator which can cause friction and a loss of efficiency. This is particularly true should oil leak into the "gap" between the armature and the rotor whereby the efficiency of the generator would be greatly reduced.
This problem is further magnified in aircraft generators which operate at high altitudes. As the altitude increases, the density of air decreases which, in essence, reduces the pressure in the isolated compartments or cavities of the generator. When the density of the air is reduced, any entrapped oil has a greater tendency to become particlized in the air and enhance the possibility of leakage between the operative components of the generator.
Heretofore, a plurality of individual, mechanical scavenge pumps have been used to withdraw oil which has leaked into respective compartments of the generator. However, as outlined above, the weight of aircraft generators is a substantial concern. Such mechanical scavenge pumps increase the weight, as well as the complexity and cost of the generator.
This invention is directed to solving these problems by providing a scavenge system which employs scavenge pumps that are lightweight, extremely simple, cost effective and, in fact, do not have any movable parts.